An important respect of biomedical engineering is researching of scaffold materials. Introducing an appropriate scaffold material is an important factor for facilitating differentiation of a cell along a desired direction and thus the formation of a tissue, which is beneficial for tissue repairing. A three-dimensional porous cell scaffold can not only accommodate a cell, a cell product and an extracellular matrix, but also be a basic cell attachment frame and a metabolism site, the morphology and functionality of which can directly affect the morphology and functionality of a tissue formed therefrom.
Bone injury and bone defect are clinically common, and the injured bone can be repaired with an endogenous bone or an exogenous bone. However, both the endogenous and exogenous bones have disadvantages such as a damage of reoperation to a patient, and thus recently there are many researches of bone tissue engineering. The scaffold material plays an important role in the bone tissue engineering, which provides a three-dimensional scaffold for cell growth and tissue repair. A desired material of a bone tissue engineering scaffold should have the following five features: (1) good biocompatibility, no cytotoxicity during in vitro culture, no inflammation and rejection reaction caused when implanted in vivo; (2) a three-dimensional structure, an appropriate porosity and aperture size, which are beneficial for cell growth, transportation of nutrients and discharge of metabolic products; (3) a good surface activity, and suitability to cell adhesion and proliferation; (4) a good degradation performance, wherein the scaffold should be gradually degraded and absorbed during tissue formation and does not affect the structure and function of a cambium; and (5) mouldability, wherein the material can be processed into a desired shape and maintain a certain mechanical strength.
Currently, the research of the porous composite scaffold mainly focuses on the composition between a biodegradable polymer and a ceramic particle having a biological activity. A biodegradable polymer (such as poly L-lactic acid (PLLA) and polycaprolactone (PCL)) has good biocompatibility, biodegradability, a great mechanical property, a controllable degradability and processibility, and a degraded product of the polymer can participate in human metabolism. This makes them become one of important materials used currently in the biomedical field, and has been approved by U.S. Food and Drug Administration (FDA) for human use.
However, carboxylic acid generated by degradation of a polyester polymer scaffold such as polylactic acid, polycaprolactone and polylactic acid-hydroxyacetic acid copolymer causes pH reduction in a tissue microenvironment, which is unfavorable for cell growth and angiogenesis (Sung H J, Meredith C, Johnson C, et al. The effect of scaffold degradation rate on three-dimensional cell growth and angiogenesis. Biomaterials, 2004, 25: 5735-5742.); and when the scaffold size is too large or the body fluid circulation at the implanted site is relatively weak, since the acidic materials generated by degradation is not buffered with enough body fluid, pH is reduced significantly, which is a hinder to the conduction of bone repair (Agrawal C M, Athanasiou K A. Technique to control pH in vicinity of biodegrading PLA-PGA implants. Journal of biomedical materials research, 1997, 38: 105-114.). Through further research, it is found that compared with that under normal physiological conditions, when pH is below 6.5 the activity of an osteoblast cell is reduced greatly (Shen Y, Liu W, Wen C, et al. Bone regeneration: importance of local pH—strontium-doped borosilicate scaffold. Journal of Materials Chemistry, 2012, 22: 8662-8670.), wherein since the osteoblast cell is used for generating new bone, avoiding a too low pH during the bone repair process is beneficial for maintaining the activity of the osteoblast cell, thereby facilitating the repair and regeneration of a bone tissue.